1. Field of the Invention
This invention relates to copolymers of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether, and, more particularly, to copolymers which are substantially free of poly(alkyl vinyl ether) homopolymers therein.
2. Description of the Prior Art
Copolymers of maleic anhydride (MAN) and a C.sub.1 -C.sub.4 alkyl vinyl ether (AVE) have been described extensively in the art. However, such copolymer products invariably include homopolymers of poly(alkyl vinyl ether) as an impurity as a result of homopolymerization of excess alkyl vinyl ether present in the reaction mixture. The presence of this poly(alkyl vinyl ether) impurity adversely affects the performance of any hydrolyzed copolymer product made therefrom, in personal and oral care compositions. Particularly, this impurity imparts objectionable color and haze to such compositions.
Accordingly, it is an object of the present invention to provide solvent-free, fine white powders of a copolymer of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether free of poly(alkyl vinyl ether) homopolymer to the extent of the detection limit of NMR analysis, which is &lt;1 molar % of the homopolymer.
Another object of the invention is to provide a solvent-free process for making such high purity copolymers.
A feature of the invention is the inclusion of a suppressor agent in the reaction mixture of maleic anhydride and excess alkyl vinyl ether and radical initiator. The suppressor agent is present therein in an amount sufficient to prevent cationic homopolymerization of alkyl vinyl ether monomer during the radical copolymerization of these monomers.
Another feature of the invention is to provide hydrolyzed copolymers of maleic anhydride and alkyl vinyl ether free of homopolymers of alkyl vinyl ether which are without color or haze.